Test and refinement of a down-scaled actively suspended forwarder

Abstract: Cut-To-Length (CTL) logging is the dominating logging method in many parts of the world. CTL logging requires a forwarder for the logs from the felling area to a landing area. Due to the harsh off-road working conditions, a well performed suspension system is necessary for the forwarder. A down-scaled forwarder prototype of the full-scale XT28 prototype was developed last year but without any control system. In this project, the forwarder was conducted to the Skogforsk standard rough ground test and development and implementation of a control system was chosen as a refinement task. Structure refinement was also achieved for the improvement of the dynamic behavior. Within the project, the down-scaled version of standard test track was realized as well. The control system with fuzzy logic control strategy was implemented to control the pitch and roll angle when passing the bumps on the track. The scaling effect was investigated with the Buckingham Pi Theorem and utilized to understand the relation between the dynamic behavior of the down-scaled prototype and the full-scale forwarder. During the test, the pitch and roll angle history were collected with a maximum angle of 8 degrees when the forwarder was moving with a speed of 0.06m/s. The test with the control system was recorded but due to the vibration it was hard to collect data in this circumstance. From the test, it is clear that the control system was able to work but its ability was limited owing to the slow reaction speed of the linear actuator. With the analysis of the real hydraulic actuator, it was implied that a better performance could be achieved if this control system was implemented on the full-scale forwarder.